Species Rarity

When scientists and decision makers try to determine and protect different type of species that may be under the threat of future extinction, there is a process that is employed in order to do so. This is done so that the species can be prioritised and the species that need the most help are helped first, thus reducing the risk of extinction. Species that have smaller populations are more prone to extinction, and generally these are the species that will be concentrated on. To determine the population of species and how they are prone to internal and external factors which affect there population is discussed in this article: Population Variability in Species. This article will discuss how scientists and decision makers classify species as to their conservation status and how these factors are determined.

Population Characteristics

When a species is declared to be rare, it means that it may have a very small population, a limited distribution, or a combination of these factors. There are three things that scientists will normally look at, and that is species abundance, species distribution and species specificity. The species abundance is measured within the normal habitat of the species and how dense the population is. The species distribution is a measure of how far the species is spread within the conditions in which it can survive, and the species specificity refers to the range of ecological conditions in which the species can survive, eg different types of terrain, weather conditions etc. When a species has a very narrow range of habitat in which it can survive, this is called a stressed site which contains rare specialised species. If the habitat is widespread but the species number is low, these are called widespread rare species and if the species are high in number but only have a very narrow range of habitat, they are called locally common species which are restricted. Penguins are a good example of this type of species 1).

Classification of rarity is required to give the best possible chance for these species to survive. These classifications can be split into three different sub groups, which are low abundance, restricted range and habitat specificity. A species can have a low abundance due to a range of different reasons, such as the lack of resources, external environmental impacts such as land clearing, disease, predation or the encroachment of invasive species into their normal habitat. Population counts are required to determine whether the species is in fact low in abundance, and these counts are required to be conducted over a longer period of time in order to remove any anomalies. Restricted ranges can be caused by factors such as an intolerance to changing climates, loss of habitat or food resources, disease, environmental barriers due to severe weather events, introduced predators or human induced factors. Habitat specificity can be due to factors such as the evolutionary process that cause the species to adapt to unusual or very unique environmental conditions, or in broader terms finding a 'niche'. Such processes cause the species to have very low populations due to there only being a very small area which it can inhabit, which in turn limits food resources and thus affect reproduction 2).


Species rarity occurs when a number of interactions occur between the fundamental niche of the species, its role within that community and the events that occur which affect its dispersal, reproduction and survival rates. Thus the biggest factor is species rarity is caused by loss of habitat due to human activities such as land clearing, farming and development. If a species is rare, it does not necessarily mean that it is endangered, it means that we should be careful as to how we deal with the habitat in which the rare species is found. Biologists will classify species that are at risk by calling them extinct, extinct in the wild, critically endangered, endangered, vulnerable or rare. Generally rare species are put into two categories, the small population paradigm and the declining population paradigm. The small population paradigms are species that have small populations concentrated into small niches, and these species are at a higher risk of extinction due to having little alternative if their habitat is lost. The declining population paradigm are species that are vulnerable to human activities, hunting, predation and loss of food sources. The species which fit into either of these categories are generally defined as rare 3).

The East African Bongo is a rare species 4)

Changes in Abundance

Undoubtedly the biggest factor in species extinction or contraction is human activity. Very few species have gone extinct in recent times due to any other cause and mass extinctions in the past are thought to have occurred due to environmental catastrophes, such as the meteor theory. In Australia, there has been significant species loss after the settlement of European people a little over 200 years ago. The rough predictions are that over 20 species of birds, 20 species of mammals and over 60 species of plants are now extinct due to human activity, along with several other species such as reptiles, insects and amphibians. This has occurred to due land clearing for farming and residential development, introduction of invasive species, introduction of predators, introduction of non native herbivores and land compaction. Despite all this, there are still cases of species decline due to non human factors and it is important that these factors are determined and then separated. Human activity has not been all bad news for all species either, with some animals thriving due to these factors, such as kangaroos, which have had an explosion in population due to the introduction of different types of grasses for grazing animals which has given them an immense increase in food which in turn resulted in increased reproduction possibilities 5).

Effects of Climate Change

Climate change is another factor that is expected to impact species populations in the future. The climate of regions governs what species can live in that certain area, right down to a micro biotic level. Most species have a very narrow range of climatic conditions in which they can survive, and each species plays an integral part in the survival or otherwise of other species. A good example of this is the chain of predation, such as the loss of polar bears may also mean a loss of fish species. This can occur due to the fact that polar bears control the number of seals in an area, and seals eat certain types of fish. If the polar bears were to disappear, seal numbers would expand rapidly, which would then mean they have a greater need for food and then cause a major impact on the fish numbers. Most species have adapted to climate change in the past through a slow evolutionary process. Unfortunately due to human activity, the climate is changing at a much faster rate than usual and this may not give most species enough time in which to adapt and evolve, leading to mass extinctions. Species which have narrow habitat ranges in which they can survive will simply have nowhere to go and eventually disappear and become extinct. There are three ways in which species can react to climate change: Move, adapt or die 6).


Polar Bears face habitat loss due to climate change 7).

A change in mean temperature of 3 degrees Celsius can have a severe impact on species distribution. When it comes to different species this change in temperature will mean that the level of ideal climate will change 300-400 kilometres in latitude and around 500 metres in altitude for animals who live on mountains or high regions. Unfortunately most species, especially ones that cannot fly, will not have the luxury of being able to move 300-400 kilometres north or south due to physical barriers such as human development or other land barriers. High dwelling species could possibly move up, but this will only place more pressure and competition for the limited resources that are already present. This means that most species will need to be able to quickly adapt and evolve or face imminent extinction. Currently in some alpine areas it has been noted that several plant species are moving upward due to a change in climatic conditions, and also changes in ocean temperatures have seen fish species starting to move towards the poles in greater numbers to seek colder water. It has also been noted that due to warming in certain areas, insects are going through their developmental cycle a lot quicker, and this may have a profound effect on agricultural yields for humans. This can also alter the way in which flowers and other plants are pollinated and possibly increase the amount of invasive species into new areas 8).

It is predicted that by the year 2050 the planet Earth will have lost almost half of it's biodiversity, and this will be due to a combination of human related activities and climate change. This will occur mainly through habitat loss either due to human development or changes in climatic conditions, increase in invasive species due to most invasive species being quicker to adapt to changes in climate which can also cause a loss of food sources for many herbivores. Whilst it may be possible to implement adaptation strategies for human settlements and hard engineering measures, it is almost impossible for us as humans to implement adaptation measures for whole ecosystems and bioregions. Perhaps one of the ways in which we can help to protect species from extinction is to reduce the amount of land clearing and increasing the amount of protected areas.


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East African Bongo by Patrick Coin, licence CC 2.5, Available: http://commons.wikimedia.org/wiki/File:Tragelaphus_eurycerus_isaaciPCCA20071227-8374B.jpg
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Polar Bear by Ansgar Walk, licence CC 3.0, Available: http://commons.wikimedia.org/wiki/File:Eisb%C3%A4r_1996-07-23.jpg
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